Motor vehicle disc brake systems utilize a disc brake unit, composed of a disc brake rotor and a disc brake caliper, at each respective wheel.
The disc brake rotor typically includes a rotor hat for connecting to an axle hub of a rotatable axle of the motor vehicle, and at least one annular rotor cheek connected to the rotor hat, wherein the at least one rotor cheek has a pair of mutually opposed braking surfaces onto which brake pads are selectively applied when braking is desired. Typically, the rotor cheek configuration may be solid, in which case a single rotor cheek has opposing braking surfaces thereon, or may be vented, in which case a pair of rotor cheeks are mutually separated by a web of ventilation vanes and each rotor cheek provides a respective braking surface so that, in combination, two mutually opposed braking surfaces are provided.
The disc brake caliper includes a generally U-shaped caliper bracket, including inboard and outboard disposed tie-bars. The caliper bracket supports a mutually opposed pair of brake pads, one brake pad disposed overlying a respective rotor cheek braking surface, wherein the caliper, the brake pads, and other associated brake components collectively form a “brake corner”. Normally, the caliper keeps the brake pads separated from the braking surfaces of the one or more rotor cheeks, and braking of the motor vehicle occurs at the brake corner by hydraulically actuating the brake pads to press upon the braking surfaces of the one or more rotor cheeks. Frictional interaction between the one or more rotating rotor cheeks and non-rotating brake pads causes braking of the motor vehicle to transpire, the rate of braking depending upon the pressure of the brake pads against the braking surfaces.
Brake squeal can be undesirably generated at the brake corner when braking occurs, particularly in the low frequency range of from about 2 kHz to about 6 kHz. This brake squeal is the result of modal excitations of the disc brake rotor (composed usually of cast iron) and the disc brake caliper by the frictional interaction of the brake pads.
With regard to the disc brake rotor, it is known in the prior art that brake squeal can be addressed by reducing modal excitation on the disc brake rotor by the selection of friction material of the brake pads (ie., lowering the frictional coefficient), by modifying the modal excitation response of the brake corner via changing the modal properties of the rotor cheeks (ie., in terms of resonant frequencies, mode shapes, and structural damping through higher carbon content of the one or more rotor cheeks and/or increasing the disc brake rotor mass, or using exotic, expensive materials), and by introducing additional damping for example via a shim disposed at a backing plate of the brake pads.
With regard to the disc brake caliper, countermeasures to reduce low-frequency brake squeal include: 1) increasing the stiffness of the caliper bracket by increasing the cross-sectional area of the tie-bars, or 2) casting in or mechanically attaching a mass to the caliper bracket, wherein the mass acts as a vibration damper and/or changes the dynamic response of the caliper bracket.
The aforementioned brake squeal countermeasures are relatively effective for most brake corner designs, but they require a significant amount of testing and analytical resources in order to be effective. And unfortunately, brake corners for performance motor vehicles, or those motor vehicles with high friction lining materials, are resistant to the prior art brake squeal countermeasures, due to the high amount of modal excitation from the friction material of the brake pads.
A breakthrough in disc brake technology, which is aimed at eliminating brake squeal originating at the disc brake rotor, is described in U.S. patent application Ser. No. 10/961,813, filed on Oct. 8, 2004, assigned to the assignee hereof, wherein the entire disclosure thereof is hereby incorporated herein by reference. In this disclosure, a Coulomb friction damped disc brake rotor is described, wherein damping of the modal excitations is provided generally coextensively with the braking surfaces of the one or more rotor cheeks. In this disclosure, the Coulomb friction damped disc brake rotor has at least one interfacial boundary formed in at least one rotor cheek which is disposed in generally coextensive relation to the braking surface thereof. In this regard, by “interfacial boundary” is meant a mechanically distinguishable surface boundary between two surfaces which are in mutual contact such that a state of Coulomb friction exists therebetween, and wherein the term “Coulomb friction” represents the energy absorption processes at the interface between two material surfaces through mechanical interaction of the surfaces, as for example temperature, pressure, time, etc. In a preferred embodiment of the Coulomb friction damped disc brake rotor according to the disclosure, an insert is disposed in at least one rotor cheek of a disc brake rotor having either a solid or vented rotor cheek configuration, wherein the insert provides mutually opposed interfacial boundaries with respect to the surrounding rotor cheek, and wherein the insert is annularly configured and disposed generally coextensively with a braking surface of the rotor cheek. Alternatively, a plurality of inserts may be provided in the one or more rotor cheeks. Alternatively further, the interfacial boundary may be provided by an interstice formed in the rotor cheek in which the surfaces of rotor cheek which define the interstice mutually form therebetween the interfacial boundary, wherein any number of interstices may be provided in one or more rotor cheeks.
What remains needed in the art is to somehow provide damping of the disc brake caliper bracket, so as to eliminate brake squeal at the disc brake corner.